The present invention relates to an optical lens, particularly relates to a secondary optical lens of a polyhedron.
Most of the lenses for current light emitting diode (LED) light projectors are total internal reflection lenses, which are in the form of a single lens, three-in-one or all-in-one lens. The lens unit of such lens comprises a substantially smooth aspheric surface for light converging positioned in the centre, a smooth total internal reflection surface positioned on an outer side, and a light emitting surface on the top which is a smooth plane surface. For light projectors requiring a large light distribution angle or light mixing, the light emitting surfaces of certain lenses are designed as a micro lens array having a honeycomb shape. These total internal reflection lenses involve some disadvantages including:                1. A light spot projected by the smooth aspheric surface for light converging positioned in the centre of the lens unit has the square shadow of the LED chip due to imaging effect, which has very poor appearance;        2. Although a circular light spot may be projected by the smooth total internal reflection surface on the outer side of the lens unit, the light spot has sometimes inconsistent color temperature in the center and at the edge based on the chromatic dispersion effect of a prism as the lens is a total internal reflection lens with small lower dimension and large upper dimension; and        3. The total internal reflection lens with the honeycomb shaped micro lens array on the light emitting surface, although having a relatively even light mixing result, has relatively poor efficiency due to the Fresnel loss from the micro lens array on the light emitting surface.        
In view of the above problems, the present invention provides a secondary optical lens, which has a plane light emitting surface, a central refraction portion having a plurality of micro lenses on the bottom surface. The present invention also provides a total internal reflection surface on the outer side adopting a diamondoid polyhedral flake design. This may ameliorate the problems of the projected square shadow from the LED chip as well as inconsistence of the color temperature in the centre and at the edge of the light spot.